There is known a farrowing pen for swine which comprises a sow's pen and a pair of newborn pens provided both sides of the sow's pen. All the known pens have an equal floor height, or the newborn pens have a higher floor level than the sow's pen since they generally have a heat insulation mat placed on the floor. Each newborn pen is divided from the sow's pen by a side fence usually comprising a pair of vertically spaced apart horizontal bars. The distance between the side fences, or in other words, the width of the sow's pen has been sufficiently large to permit a sow to stand up or lie down easily.
In such a farrowing pen, when a sow lies down, a piglet was sometimes pressed to death under its mother, or when the sow would stand up, she sometimes kicked or trod on a piglet with her hind leg, and caused it to die. The death of piglets from the pressure of their mother has long been a serious problem. More complete separation of the newborn pens from the sow's pen, provision of heat insulation mats in the newborn pens, and other measures have, therefore, been taken to keep piglets away from their mother. Nevertheless, a large number of piglets are still crushed, and swine producers have difficulty in protecting piglets.
A sow lies down when suckling her piglets. She usually offers the upper row of nipples to her piglets first, and then, the lower row of the nipples. Accordingly, it is impossible for all the piglets to take the mother's milk at a time, resulting in a difference in the rate of their growth.